The log1p() function computes log_e(1.0 + x). The value of x must be greater than -1.0.

Upon successful completion, log1p() returns the natural logarithm of 1.0 + x.

If x is NaN, log1p() returns NaN.

If x is less than -1.0, log1p() returns -HUGE_VAL or NaN and sets errno to EDOM.

If x is -1.0, log1p() returns -HUGE_VAL and may set errno to ERANGE.

For exceptional cases, matherr(3M) tabulates the values to be returned as dictated by Standards other than XPG4.

The log1p() function will fail if:

EDOM

The value of x is less than -1.0.

The log1p() function may fail and set errno to:

ERANGE

The value of x is -1.0.

See attributes(5) for descriptions of the following attributes:

log(3M), matherr(3M), attributes(5), standards(5)